1. Field of the Invention
This invention relates to surgical instruments, used to bite out or cut portions of bone or cartilage, and specifically to those of the Kerrison type, or similar type.
2. Description of the Related Art
Rongeurs are surgical instruments for the cutting away of human tissue, and most commonly, cartilage and/or bone. Kerrison rongeurs are utilized in spinal surgery to remove bone and to thereby gain access to the spinal canal. These rongeurs typically have a closable jaw, one member of which having a cutting end and the other member being a foot plate which must be placed beneath the tissue, generally bone or cartilage, to be cut.
For example, when a Kerrison rongeur is in use, the surgeon places the bone to be cut, such as the leading edge of the lamina of a vertebrae, within the open portion of the distal end of the rongeur. The surgeon then squeezes the handle of the rongeur which causes the moveable jaw member of the rongeur to be advanced through that portion of bone to reach the foot plate, and thereby amputating that portion of bone. Once the jaw members become full, the rongeur must then be completely removed from the surgical site and passed to the scrub nurse for the removal from the instrument of that cut portion of bone.
To facilitate the necessary function of the rongeur, the foot plate is generally cupped, as is the cutting end of the moveable jaw member. If only the moveable jaw member were cupped and the foot plate flat, then upon cutting with such an instrument the bone would be so compacted into that singular cup as to make it nearly impossible to remove the portion of bone cut. However, because the foot plate of the Kerrison rongeur is below the lamina and proximate to the dural sac, spinal cord, and nerve roots, there is a compelling need to avoid any excessive thickness of the foot plate itself. Therefore, the foot plate cup is generally not quite as deep as the cup in the moveable jaw member and thus, even in the double cup design, the cut portion of bone tends to be compacted proximally, making its removal nevertheless difficult. The removal from the instrument of the cut portion of bone often requires that the scrub nurse use a small rigid hook, or toothed forceps, and often further requires that the physician temporarily relinquish the instrument entirely to make such bone removal possible. Once cleaned, the instrument is returned to the surgeon who, in returning it to the surgical site, must then reorient himself to the task at hand. This sequence must then be repeated over and over again with each cut of bone. Typically, such spinal procedures unfortunately require many such cuts.
Essentially flat foot plates had been in use earlier this century, but proved to be undesirable because the opening of the jaw members to be able to get around the thickened portions of the vertebrae tended to exceed the capacity of the cup in the moveable jaw member and the bone cut would be markedly compressed during the cutting process. When the foot plate is flat, the mass of bone bitten is forcefully compacted into the singularly cupped recess of the movable jaw member such that it is extremely difficult to remove that bone after each cut.
A consideration of the structure and function of the prior art rongeurs, and specifically in regard to the foot plate structure and its requisite thickness, is quite revealing. It would appear that in use the foot plate is subjected to five types of forces.
Consistent with its intended purpose, the foot plate is subjected to, and must withstand, that force necessary to actually cut through the bone, which shall be referred to as the Bone Cutting Force. However, the surgeon has no way of knowing what that force is, or even when he has reached or exceeded it. Accordingly, the foot plate is invariably exposed to a second force significantly greater than the Bone Cutting Force which shall be called the Terminal Squeezing Force. The Terminal Squeezing Force occurs after the bone fragment has been cut and is caused by the surgeon generating force in excess of the Bone Cutting Force. This results in the relatively massive slide portion of the instrument being driven with great mechanical advantage against the foot plate. This occurs because the manufacturer of such a rongeur must allow for wear of the cutting surfaces and still allow for the jaw to still be able to close such that the slide portion of the instrument has a greater excursion than would be otherwise required to merely close the jaw members of the rongeur when the cutting surfaces are new.
A third force encountered by the foot plate is a product of the fact that the instrument jaw generally opens to an extent greater than the combined depths of the cups such that the solid bony contents are physically crushed. This is the Bone Crushing Force, and again is additional to the Bone Cutting Force.
A fourth force that may impact upon the foot plate is that which occurs when the jaws of the rongeur encounter an object, which because of its physical structure, is unbiteable. In this situation, while the jaw is still in a relatively open position, again a force greater than the Bone Cutting Force is generated and in this case is then transmitted through the unbiteable object to the foot plate.
The fifth force to which the foot plate is subjected is leverage. When the jaws are not sufficiently sharp, or are worn such that they fail to completely close, then the bone will not be completely cut through, and the surgeon will rock the instrument back and forth to fracture through the remaining bony bridge. In this situation, the angle of the jaw in contact with the leading edge of the lamina becomes the fulcrum point and the foot plate, measuring generally less than half of an inch in length, is one lever arm, while the remainder of the instrument through the shaft and handle is the other. Since these instruments generally measure on the order of approximately 10 inches, the mechanical advantage, or force applied to the tip in a rocking maneuver is on the order of magnitude of 20 to 1.
The ability to safely withstand repeated exposure to these five forces, and the previously discussed need to cup the inner surface of the foot plate, have in the past, determined the requisite thickness of the foot plate.
At present, there is also a need for a rongeur with a capacity to remain within the wound and to repeatedly bite bone and to store the bone bitten until all the requisite bone removal has been completed without the need to continuously remove the rongeur from the wound for the purpose of removing the cut portion of bone from the instrument to clear the cutting edges. A further and related need exists for a rongeur that would collect and contain all of the bitten material such that the delicate neural structures would be protected from contact with the bitten material and/or any cogenerated inadvertent debris. In this regard, any rongeur can bite more than once, but not properly. That is, one could deliberately take several small bites, each of which would fail to fill the cup in the foot plate and the singularly cupped recess of the moveable jaw member, in lieu of taking one full bite. However, once the cup in the foot plate and the cupped recess of the moveable jaw member are filled, further biting is not possible. Bone may be crushed as cups that are already full approach one another, but their contents will shield any further interposed bone from the cutting edges, thus making any further bone cutting impossible.
An example of a multibite rongeur is shown in U.S. Pat. No. 3,902,498 issued to Niederer on Sep. 2, 1975. Niederer teaches the use of a rongeur hollow at the tip such that it is possible to take several bites. Unfortunately, since the hollow tip is open to the wound at both ends, the further use of the instrument pushes the already bitten material out of the other end of the hollow tip and back into the depths of the surgical wound where it can cause great harm. This shortcoming of Niederer can not be overcome by simply closing off the second opening as the operation of the instrument requires the second cutting member (8) to pass through the same area that the ejected bone had occupied.
Further, if a rongeur could take and then store safely, multiple full bites of bone, a rationale would then exist for a power rongeur. A prior art power rongeur was marketed by the 3M Company. However, it was very bulky and required a large bore hose connection to a non-sterile compressed gas tank making the instrument very unwieldy. The biting mechanism itself was rather slow and clumsy and the instrument still required removal from the wound after every bite to clean out the bitten portions of bone.
There is also a need for a disposable cutting means so that those portions of the rongeur involved in the actual cutting may be easily renewed as these portions of the rongeur rapidly wear and dull from the cutting of bone. With wear comes both edge dullness and non-mating of the contact surfaces rendering the rongeur ineffective and even dangerous as it fails to cut cleanly and begins to rely on tearing.
Both U.S. Pat. No. 3,902,498 issued to Niederer and U.S. Pat. No. 5,026,375 issued to Linovitz et al. disclose a means for replacing the cutting element on just one side of the jaw in a rongeur appearing to have cutting cupped portions on both sides of the jaw. Since dulling and wear occurs equally on both sides of the jaw, replacing only one side is obviously ineffective in restoring the sharpness and the full cutting function of the instrument or for even providing for the proper mating of the cutting surfaces as one new side is then opposed to one worn side.
Reference is made to U.S. Pat. No. 4,722,338 to Wright et al. and U.S. Pat. No. 4,777,948 to Wright et al. U.S. Pat. No. 4,777,948 discloses a rongeur having a stationary hollow tubular cutting element 28 which may be removably attached to the rongeur. The entire assembly must be disengaged to replace the cutting element. The device is not capable of taking multiple full bites since only a short recess is provided for pulling the severed bone into the hollow cutting tube and contrary to that concept teaches that the bone is then ejected after each cutting operation, as explained in U.S. Pat. No. 4,722,338 at Col. 3, line 10. No collection of the cut bone is achieved by the hollow cutting element beyond a single cut and the cut bone is then ejected. In fact, the cut bone may be ejected into the wound, which could cause great harm.
Finally, there is a need for a Kerrison type rongeur that is capable of taking larger bites of bone than is now possible. While the need for such a rongeur exists, by prior art technology the foot plate would be too thick to safely use beneath the lamina, and the surgeon would lack the strength to crush and compact that volume of bone.
There is therefore a need for a Kerrison type rongeur with a thin, but strong, foot plate that would be able to take and safely store throughout the operation multiple full bites of bone. Such a rongeur would also have at least a disposable cutting element system capable of replacing all cutting edges to provide for the surfaces of the cutting edges to be sharp and close perfectly and would be capable of taking larger bites of bone than previously possible. Such a rongeur could be powered without the need for external connections to a remote power source.